The present invention relates to an apparatus for measuring the velocity of an enzyme reaction used for the activity measurement of an enzyme or the quantification of a chemical substance.
An enzyme acts as a catalyst in a chemical reaction. Such a chemical reaction is called "an enzyme reaction". The activity of the enzyme is the velocity of the enzyme reaction, the activity measurement of the enzyme is the catalytic function of the enzyme, i.e., to identify the effective quantity, and fundamentally has an important meaning in the case of handling the enzyme.
A process for measuring the activity of an enzyme heretofore or a process for measuring the quantity of a chemical substance in a specimen includes an electrochemical process and an optical process.
A process for electrochemically detecting the quantity of a substance produced or erased by an enzyme reaction using an immobilized enzyme in a column is known as the electrochemical process. In this process, the enzyme can last for a long time, and the enzyme reaction is stable. However, since a change in the quantity of chemical substance is detected at an outlet of the column, the process can detect the quantity only by an end assay but is improper for a rate assay.
Another known electrochemical process is to dip enzyme electrodes in a specimen. In this process, carriers immobilized with the enzyme are arranged at the enzyme electrodes. This process can perform a rate assay. However, it cannot measure the activity of the enzyme while continuously flowing a substrate solution, and it merely measures the activity of the enzyme by creating the enzyme reaction in a discrete or batch manner. Further, since it is necessary that the substance which increases or decreases in the immobilized enzyme diffuses in the carrier of the immobilized enzyme to reach the surface of the electrode in case of detecting the reaction substance, the responding time of the electrode depends upon the diffusing distance in the carrier. Therefore, it is necessary to reduce the thickness of the carrier made of a membrane so as to accelerate the responding time of the electrode. Then, the enzyme electrode cannot last long, and becomes unstable. In addition, its sensitivity is low.
In an optical process, a reaction product produced by an enzyme reaction is supplied to a flow cell. The substance and a luminescent substance react in the state kept in the flow cell. The fluorescence or chemiluminescence is detected to obtain the quantity of a chemical substance. This optical process has a high detecting sensitivity, but this process can perform only an end assay. Since this process measures the reaction substance by stopping the substance in the flow cell in the same manner as the electrochemical process, the process can measure only in a discrete manner. To stop the reaction substance in the flow cell for this purpose, a three-way valve or the like must be provided in the flow passage. The use of such a valve not only makes the system complex but also may cause problems. In a batch system like this, a pause must be taken after each step of measuring which is a waste of time.
In the chemiluminescence, a pH range adapted for the enzyme reaction and a pH range adapted for the chemiluminescent reaction may differ. In this case, the activity of the enzyme cannot be measured. Therefore, the optical process by the chemiluminescence cannot always be applied to the activity measurements of all enzymes.